Question regarding best limit for blinds

Newbie, and looking to find the best limit for our blinds when playing with (on average) 7 people with $7,070 to start totaling $49,490 on the table. We have been playing 20 minute intervals up to 250/500 blinds and then cutting down to 15 minute intervals from there and stopping at $4,000/$8,000 blinds. However when we get to $4k/$8k blinds it seems after just a few hands someone ends up all in and the end of the game is based more on the luck of the draw then any strategy. Based on our table amount, what do you feel is the best blind limit and is our 20/15 minute intervals ok. FYI, we keep it 20 minute intervals in the beginning b/c we play every weekend amongst neighbors and figure the 20 minutes gives everyone a longer time to play together before people start getting out.

Thanks for any help.

You start with 14 BBs among 7 people? It's a crapshoot to start if that's right.

vcpoker starts tourneys with 2k chips, 20-40 blinds
pokerroom starts with 1.5k chips, 10-20 blinds

so go from there