Read this: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/networking_guide/sec-using_channel_bonding
Does your switch support link aggregation? Try change hash policy, arp_interval.
In templates created like that You changing only vm configuration, and create next snapshot. High number of snapshots can slowdown storage. I see no advantage with creating templates from templates changing only resources, and options.
If You want run PVE from flash devices You can run it as live system without persistence.
I've test setup (on production envoirment - we want to move from ESXi) running like this from sdcard with uptime around 300days. PVE have overlayfs with 1GB storage in RAM and after that time it uses around...