Hi Hayley (WARNING - THIS GOT VERY LONG!)
It seems you have unwittingly encouraged his late bedtime and also he is rewarded by getting to sleep in your bed. Does he have his own cot/bed? A cot would be ideal since he would be more likely to stay in it than a bed. Perhaps that is part of the problem, he is too easily able to "escape" the bed and consequently the bedtime! If he doesn't have one, make a big thing out of going to choose either a cot or bed. If he does have one, make it special to him by letting him choose a blanket or comforter or toy.
I think the other problem is lack of an established routine - you say yourself that you "gave up" when he was 8 months old. That's a shame, since you've just made it harder to break his bad habits now! All is not lost though, so don't despair. BUT you will need to persevere and be strong and tough with him - sounds like he's the boss of bedtime when it should be you!
Your son needs to learn to fall asleep by himself, preferably in his own bed or cot, unless you feel strongly about him sharing your bed.
I think the controlled crying thing at this age would be worth a try, but you would need to be really determined to see it through. I tried this with my dd at around 10 months as she kept waking for a night feed, which I knew she didn't really need. I didn't do the whole "don't touch them or talk to them or pick them up" thing, but I would just pat her bottom and say "time to sleep now, shhh" etc, then as soon as she calmed even a little I would leave, lengthening the gap each time before I went back in. At 15 months you will either need a cot or a doorgate to stop him simply running away from you! Expect a lot of yelling, possibly hitting etc, as he will be angry at this change in routine. But know that it will only be for a few nights and will make life easier and bedtime more enjoyable for both of you!
Initially I think it would be best to try the gentle approach suggested by someone else (lost the page now), and stay in his room after you put him to bed. You could even put a bed or mattress for yourself in his room and stay until he goes to sleep. Pretend to be asleep and do not go to him, though...again you will still need to be tough! But it is less heartwrenching than the true controlled crying method! Encourage and praise any little progress he makes and don't let him slip into old habits, not even for just one night, or he'll think it's worth a try another night!
Once you have settled him in his own room, I would add/continue the following:
Set a regular bedtime and stick to it - any time between 7 and 8pm is reasonable. (You might need to gradually bring your son's closer to this time, by putting him to bed 15 to 30 mins earlier every night for a fortnight or so.) Develop a routine that is easy for you and your son to follow, eg change nappy, brush teeth, read story, go to bed, stay in bed til morning. Tell your son half an hour before bedtime that it will be bedtime soon. You can even set the oven or microwave timer to be a reminder signal. You could reward going to bed well by reading an extra story in bed or singing a quiet song.
When you say goodnight and leave, ignore any requests or protests, or at least delay your return!!!
YOU CAN DO IT HAYLEY - AND SO CAN YOUR SON! Good luck, let us know how it goes!