This is exactly what I'm currently jumping into as a 'new' dev. I've been coding for about 3-4 years, am working on an ANCIENT php in-house ERP (we're still running v5!), and find the technical debt/unneeded complexity more shocking by the day. I've been in this position 3 months and feel like I've barely even scratched the surface of what is going on under the hood.

Teaming up for training is absolutely crucial at this time.