Update tensorflow to 2.15 in requirements.txt

Change-Id: I5981f063734acb0f141eb5379d844af15756e295
Signed-off-by: Jonny Svärd <jonny.svaerd@arm.com>
diff --git a/requirements.txt b/requirements.txt
index 0a2d9fc..f23e2c9 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
 ethos-u-vela
 pillow
 pyelftools
-tensorflow==2.14
+tensorflow==2.15