I beat MQ at about level 20, starting at 15.... Is that bad? I was thinking of starting a new person and not rushing through MQ and taking my time.

Depends.

I deleted my first true playthrough primarily becase I beat the MQ at 30, and didn't do much exploring, which I regret, due to the Fast-Travel option. Now I'm about the same level, and I'm not even halfway through the MQ.

it took you until 20 to beat it?

Do no-or-limited-fast travel, and your gaming experience will be much better.

Unfortunately, the game is meant to be rushed through multiple times. It is actually best to pick new factions/guilds/quests to do each play through and just go through the MQ quickly. The game starts to take a nosedive the further you progress. I find that after 25, and really after 30 the game is so trivialized and is painful.

id start again and get to the point where you learn to shout. then take your time and do random side quests and explore. im at 300+ hours by doing this on one character

Not really, you get more value if you play it till a reasonable level and then start over, try new character builds and playstyles. (I can't understand how people can play beyond level 40)
If your one for roleplaying think of it like this, your not going to be able to be the best thief in Skyrim all the while moonlighting as the Harbinger.
...
But, more importantly, if you enjoyed rushing then its not bad.

I don't think its bad, but that is just my opinion.

I beat the MQ at level 11

Nah, its probably the best thing you could have done. Any later than 20, and the whole MQ experience is a letdown

If you enjoyed it, it's not bad. Personally, the first thing I did in Morrowind, Oblivion, and Skyrim on my very first playthroughs at their releases was rush through the main quest so I couldn't have it spoiled and so I understood the games better. I leave things like roleplaying, self-restrictions to keep difficulty, etc to all of my other playthroughs after, with my first being a "test drive" completing as much as possible as fast as possible.

It also might have felt a lot easier than it should be if you waited any later. Level 15 - 20 is where the game is starting to become less difficult, as you get all of your skills to a respectable level and your crafting more usable.

MQ is just another quest really. It's not like Skyrim is over if you haven't done the thieves guild, companions, nightingales, daedric quests, civil war, tons of side quests, etc.
MQ is fun, but it's not the best part of the game.

True.

Well if the MQ is not lvl'd like the civil war, the sooner the more of a challenge it will be but if you wait till lvl 40 or so.

I generally like to lvl a character, just exploring, looting and doing some misc quests up till the point I feel my character has developed. Then I will do the quests lines I planned for that character.

I just hit level 50 last night and still have yet to finish the MQ. In fact I'm not even sure how far into the MQ i am. Its also my first play through of the game. I decided that my character should know the land, know the people, and be the hero skyrim needed. To do that the MQ and all other world shaping quests would have to wait.

By rushing the game you are not going to miss much because of the lack of interesting content.

You know with you screen name I can't take anything you say seriously lol