Okay, try to manual make your Render class:
https://github.com/Cadiboo/Example-Mod/blob/1.15.2/src/main/java/io/github/cadiboo/examplemod/client/render/entity/WildBoarRenderer.java
And you don‘t really need the Enderslime model, as it was the same as the Slime model: delete this class and extends in your EnderslimeRenderer class MobRenderer. First parameter was the Entity (not Entitytype) and the second parameter was the Slimemodel. If you need to add a parameter to the Slimemodel then try to add the same Entity class. In others words, see Cadiboo Github link above (don‘t add a layer, slimes don‘t have layers).