Micromanaging partner

We are a start-up working on a few projects and trying to build some strategic products alongside. This is a 3 member partnership setup with a development team of about 15 people. One person, let's call him P1 looks at commercial & tactical marketing. The other one let's call him P2, takes charge of strategic marketing. Both P1 & P2 are actually hard workers and have made some progress in business on their part, though they had no big exposure.

Having worked in a few multi-national companies before and after merging a failed start-up (2 years effort), I joined their partnership on invitation to manage the technology team and it is going for the past few months. The problem is it feels too stifling/difficult-to-breathe place as P2 keeps micro managing everything. Both P1 & P2 are supposed to be taking care of marketing & commercial aspects of business. But P2 keeps micromanaging on my area, giving me advice on every aspect of how to do project, technology discourses(though he is not capable of doing so).

The problem is that P2 has some idea and view of everything and so tends to think that he knows everything and others don't. I might make mistakes as well and I am ready to take in suggestions, but when it comes with a discourse for 30 minutes every time and on every aspect, it gets tough. Sometimes it even comes to some personal levels, which I have clearly nipped at bud. The other partner P1 doesn't feel uncomfortable as he considers P2 to be his mentor.

Are there some efficient ways of telling them not to poke too much?

"Are there some efficient ways of telling them not to poke too much?"

Yes, just tell them.

Be blunt, but polite. Dancing around it isn't usually helpful. You're already keeping it to business and not personal, so you're probably going to do well with the conversation.

There are a couple of different approaches ... one is to designate a formal time (eg 360 appraisal) so when the critique comes, you can say to table it until the designated time.

Another approach is to formalise it along lines of de Bono's 6 Thinking Hats (best in group situation). If it is visually revealled he is entering into Blue Hat thinking then he may self-correct or at least you have others pointing out he is wasting time.

A third somewhat snarky way is to overload him with more work so there's no time to waste.