No - they are very different. 'Let's go' is a suggestion - that you and those you are speaking to leave. 'Here we go' can be a couple of things. It can be an expression of realisation, and it can be a statement that you have started to go - probably with a degree of surprise, such as if you had waited for a while. In short - One is a suggestion to go, the other is a statement that the 'going' has started.

I agree with the above. Also, sometimes "here we go" is used sarcastically. Like if you are at a meeting at work and a very annoying person who always talks forever in meetings start talking, you may say quietly to your friend "here we go" and roll your eyes . . or "here we go again . . " meaning your are irritated.

"Here we go" -- conclusion "Let's go" -- suggestion