diff --git a/Dockerfile b/Dockerfile
index 3ea6fd03e3..7c33e364b1 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -153,10 +153,12 @@ ARG WITH_HELM=true
 ARG WITH_GIT=true
 ARG features=""
 
-# The version new instances start on: PyVAlias::NEW_INSTANCE in the backend. Instances keep
-# the version they were initialized with, so when raising it, keep installing every earlier
-# value alongside it.
+# Instances keep the Python version they were initialized with, so both are preinstalled:
+# LATEST_STABLE_PY is what instances initialized before the version was raised are on
+# (PyVAlias::default() in the backend), NEW_INSTANCE_PY the one new instances start on
+# (PyVAlias::NEW_INSTANCE). When raising the latter, keep installing every earlier value.
 ARG LATEST_STABLE_PY=3.12
+ARG NEW_INSTANCE_PY=3.15
 ENV UV_PYTHON_INSTALL_DIR=/tmp/windmill/cache/py_runtime
 ENV UV_PYTHON_PREFERENCE=only-managed
 
@@ -249,6 +251,7 @@ RUN curl --proto '=https' --tlsv1.2 -LsSf https://github.com/astral-sh/uv/releas
 # timestamps or Python's mtime-based .pyc invalidation discards these compiled files.
 RUN UV_CACHE_DIR=/tmp/build_cache/uv UV_PYTHON_INSTALL_DIR=/tmp/build_cache/py_runtime uv python install 3.11 --compile-bytecode
 RUN UV_CACHE_DIR=/tmp/build_cache/uv UV_PYTHON_INSTALL_DIR=/tmp/build_cache/py_runtime uv python install $LATEST_STABLE_PY --compile-bytecode
+RUN UV_CACHE_DIR=/tmp/build_cache/uv UV_PYTHON_INSTALL_DIR=/tmp/build_cache/py_runtime uv python install $NEW_INSTANCE_PY --compile-bytecode
 
 
 RUN curl -sL https://deb.nodesource.com/setup_24.x | bash -
diff --git a/backend/windmill-common/src/worker.rs b/backend/windmill-common/src/worker.rs
index 8d7662722d..6dd87f2153 100644
--- a/backend/windmill-common/src/worker.rs
+++ b/backend/windmill-common/src/worker.rs
@@ -2917,7 +2917,7 @@ impl PyVAlias {
     /// What the server writes into `instance_python_version` when it initializes an instance.
     /// Raising it also means the images must keep preinstalling every earlier value, or
     /// instances that started on one download their runtime on first use.
-    pub const NEW_INSTANCE: PyVAlias = PyVAlias::Py312;
+    pub const NEW_INSTANCE: PyVAlias = PyVAlias::Py315;
 
     pub fn all<T: From<PyVAlias>>() -> Vec<T> {
         use PyVAlias::*;
diff --git a/backend/windmill-worker/src/python_versions.rs b/backend/windmill-worker/src/python_versions.rs
index 7f9a9448f7..2166383df7 100644
--- a/backend/windmill-worker/src/python_versions.rs
+++ b/backend/windmill-worker/src/python_versions.rs
@@ -14,6 +14,7 @@ use tokio::{fs::DirBuilder, process::Command, sync::RwLock};
 use uuid::Uuid;
 use windmill_common::{
     error::{self, Error},
+    global_settings::{load_value_from_global_settings, INSTANCE_PYTHON_VERSION_SETTING},
     worker::{try_parse_locked_python_version_from_requirements, Connection, PyVAlias},
 };
 
@@ -256,7 +257,23 @@ impl PyV {
         conn: Option<Connection>,
     ) -> Self {
         let mut err = None;
-        let pyv = match INSTANCE_PYTHON_VERSION.read().await.clone() {
+        let mut setting = INSTANCE_PYTHON_VERSION.read().await.clone();
+        // A worker that loaded its settings while the server was still initializing the instance
+        // read no version, and may have started listening for setting changes only after it was
+        // written. Jobs only exist once it is, so reading it here settles that worker for good.
+        if setting.is_none() {
+            if let Some(Connection::Sql(db)) = conn.as_ref() {
+                setting = load_value_from_global_settings(db, INSTANCE_PYTHON_VERSION_SETTING)
+                    .await
+                    .ok()
+                    .flatten()
+                    .and_then(|v| serde_json::from_value::<String>(v).ok());
+                if setting.is_some() {
+                    *INSTANCE_PYTHON_VERSION.write().await = setting.clone();
+                }
+            }
+        }
+        let pyv = match setting {
             Some(v) if &v == "default" => PyVAlias::default().into(),
             Some(v) => pep440_rs::Version::from_str(&v).unwrap_or_else(|_| {
                 let v = PyVAlias::default().into();
diff --git a/docker/DockerfileSlim b/docker/DockerfileSlim
index a37ced0eca..085b3540a8 100644
--- a/docker/DockerfileSlim
+++ b/docker/DockerfileSlim
@@ -30,6 +30,7 @@ FROM ${DEBIAN_IMAGE}
 
 ARG APP=/usr/src/app
 ARG LATEST_STABLE_PY=3.12.13
+ARG NEW_INSTANCE_PY=3.15.0
 
 # UV configuration
 ENV UV_CACHE_DIR=/tmp/windmill/cache/uv
@@ -65,6 +66,7 @@ RUN curl --proto '=https' --tlsv1.2 -LsSf https://github.com/astral-sh/uv/releas
 # under the read-only nsjail runtime mount (uv >= 0.9.25). The copy below MUST preserve
 # timestamps or Python's mtime-based .pyc invalidation discards these compiled files.
 RUN UV_PYTHON_INSTALL_DIR=/tmp/build_cache/py_runtime uv python install $LATEST_STABLE_PY --compile-bytecode
+RUN UV_PYTHON_INSTALL_DIR=/tmp/build_cache/py_runtime uv python install $NEW_INSTANCE_PY --compile-bytecode
 
 # Copy to final location with world-writable permissions for arbitrary UID support
 RUN mkdir -p /tmp/windmill/cache && \
diff --git a/docker/DockerfileSlimEe b/docker/DockerfileSlimEe
index 687b1506ce..7a2483067f 100644
--- a/docker/DockerfileSlimEe
+++ b/docker/DockerfileSlimEe
@@ -30,6 +30,7 @@ FROM ${DEBIAN_IMAGE}
 
 ARG APP=/usr/src/app
 ARG LATEST_STABLE_PY=3.12.13
+ARG NEW_INSTANCE_PY=3.15.0
 
 # UV configuration
 ENV UV_CACHE_DIR=/tmp/windmill/cache/uv
@@ -65,6 +66,7 @@ RUN curl --proto '=https' --tlsv1.2 -LsSf https://github.com/astral-sh/uv/releas
 # under the read-only nsjail runtime mount (uv >= 0.9.25). The copy below MUST preserve
 # timestamps or Python's mtime-based .pyc invalidation discards these compiled files.
 RUN UV_PYTHON_INSTALL_DIR=/tmp/build_cache/py_runtime uv python install $LATEST_STABLE_PY --compile-bytecode
+RUN UV_PYTHON_INSTALL_DIR=/tmp/build_cache/py_runtime uv python install $NEW_INSTANCE_PY --compile-bytecode
 
 # Copy to final location with world-writable permissions for arbitrary UID support
 RUN mkdir -p /tmp/windmill/cache && \