[Old_Thrashbarg]

Exactly, you owe them your labor while they're still paying you. If they gave you a signing bonus or something under the assumption that you'll stay for a certain amount of time, then they will probably (justifiably) crawl it back.

Like another person said, there are people who enjoy modernizing codebases (I sometimes do myself), but if you are hating your job, do everyone a favor and make a change.

You should probably start with your manager, and explain why you are considering leaving.