Proxmox update bumped the kernel to 5.15 today.
I see the 5.13 kernel but not the 5.15 kernel even with the pvetest repo enabled. Where are you seeing it?
aaron@omv6dev:~$ apt-cache search pve-kernel
pve-firmware - Binary firmware code for the pve-kernel
pve-kernel-5.10.6-1-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.0-1-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.12-1-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.17-1-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.21-1-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.22-1-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.22-2-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.22-3-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.22-4-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.22-5-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.22-6-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.22-7-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11.7-1-pve - The Proxmox PVE Kernel Image
pve-kernel-5.11 - Latest Proxmox VE Kernel Image
pve-kernel-5.13.14-1-pve - The Proxmox PVE Kernel Image
pve-kernel-5.13.18-1-pve - The Proxmox PVE Kernel Image
pve-kernel-5.13.19-1-pve - The Proxmox PVE Kernel Image
pve-kernel-5.13 - Latest Proxmox VE Kernel Image