There is no low level. But if you wanto survive Dragonspyre without dying every couple bosses you should do your side quests and get to level, like, 50!
If you made it there by doing quests, you are just fine. People who do all the side quests might be a higher level when they start Dragonspyre, but it's not a necessity.
If you find yourself struggling a bit, a suggestion might be to do some lower side quests you hadn't done yet to gain a level or two. It can make a difference.
As a rule, I do all the side quests through the end of Dragonspyre, because I know Celestia makes a big jump in fighting the bad guys and you want to make sure you are at least level 50 when you get to Celestia so you can buy gear with critical and critical block.
I'm a level 41 in Dragonspyre. my friends are telling me that I am too low of a level to be there. So am I too low to be there?
Relax. You will find out quick enough if you're too low a level to be there. If you are dueling/questing and not getting clobbered, you're fine. Just take your time and have fun.