I am going to be patching a few assets in the next update that will hopefully lower the memory of Hellspawners first level, this should hopefully help with opening performance.
I would recommend turning off particle effects and blood effects in the games settings before starting too as the makes the experience a little less intense on direct graphical performance. Setting frame count in the settings to 30 frames may also help in performance as well.
I aim to fix this as soon as I can and I hope you stick around for the conclusion to Hellspawner coming soon :)