The only way that RAH can "collect" on the money (assuming you don't pay) is by serving you a summons and appearing in court...
This first letter is just an attempt to inform you of payment. After letting the deadline pass the only next step for them to take is serving you a summons..... This has to be done in person (they cannot mail you a summons regular mail). Either by law firm or certified mail..... You can make it difficult for them!
So logically you have to decide what the chances are they #1) find you in whatever city you are in...
And what are the chances they take it all the way to court...
I wouldn't pay for a lawyer until the time they actually serve you papers...
Training contracts are generally enforeceable assuming nothing was "promised to you" that didn't occur. There was a Flexjet pilot who fought this by way of not upgrading when they said he would. He won but it probably cost him more in lawyer fees than it would have to not fight it.
I signed a training contract back in the day at a charter co. Left a year early, and decided not to pay. They served me papers and it went to court. We settled out of court for slighly less than the original amount. However, if I had moved and they could not find me, then I would have been off the hook.