To be honest 30-40 minutes at that age
is at the long end of the spectrum. Usually a newborn starting at that length of time would have naturally developed a more efficient technique and speeded up. However there is a massive range of normal when it comes to babies and in that sense I wouldn't say it wasn't 'normal'. It's normal for her and you've obviously been a successful breastfeeder.
A few questions:
Is she actively swallowing that entire time? i.e. do you think she could still be staying on for comfort sucking? (do her sucks get lighter and fluttery towards the end?)
I would say that the 2 hour feed is almost certainly about comfort and connecting with you and perhaps connected to tiredness. Perhaps the beginning of separation anxiety is just kicking in.
Does she seem satisfied and content at the end of a feed? Are you satisifed she's getting enough wet nappies (6 in 24 hours)
Have you ever had any concerns about your latch? Does she have a big wide gape? Are your nipples ever sore?
As for starting solids - good for you for following the recommendations on waiting. However 5.5 months isn't very far from 6 months. I don't think you'll find solid food will make an enormous difference to her milk intake - infact it shouldn't as early solids is just about first tastes and a learning experience not packing in calories.
I would say you could consider breast compression
http://www.kellymom.com/newman/15breast_compression.htmlor asking someone to check your latch
or offering something else for comfort
or putting your feet up and enjoy it while it lasts (not very helpful I know but she'll be trying to borrow your mascara before you know it and it's actually very lovely you've got the patience to let her feed that long!)