Synology RS2423RP+ and VMs on it. - Really slow and not usable

Hey everyone. A few months ago i bought a Synology RS2423RP+ for my homelab. My idea was, that this expensive peace could be used as storage and as well as hypervisor. (According to the Synology website it is certified for VMs). So i tried it... but it is horrable slow. I tried all the tricks online with tuning the Storage Controller, but as fas as I found out, the problem is btrfs... Also it seems that i can't create a "fat-vm storage disk" only thin-provisioned.. and maybe this is also a problem.

What are your experience in such setups? Do i need to buy a "real server" or is there something i could do?