Try completing your milestones before giving up, those usually give you good level boosts and might bump you up alot. Normally the way destiny works is its pretty easy to level up to a point then you hit a wall that slows you right down, not sure where the level wall is with the new expansion but I dount it would be slow low that you couldn't get to up main story level soon enough.I'm not sure I want to bother, honestly. I specifically didn't do the grindy bits at the end of the last expansion. If I'm forced to do them before I can even start this one, I will pass.
I just did two public events and an adventure in ~30 minutes and went from 255 to 257. I know I can't linearly measure from that but it'd probably be at least 10-15 hours to hit 310. 255->310 is a huge amount to grind through when no story content was added for that range.