I've been running for about six months and have done a few easy 15k runs lately.  I find them too boring to be enjoyable, but otherwise not particularly challenging.  However, I'd like to be *able* to do a longer run and have the confidence to know I can do it if I want to.  Would it be practical to do an easy half marathon say once a month, but otherwise to restrict my runs to 10k (the distance I enjoy most).  

I'm mostly running for weight loss, fitness and enjoyment, rather than performance (I'm not interested in racing, except an occasional park run), so I am primarily concerned about injury risk (I am in my mid 50s, no longer overweight and in reasonably good health) and any other potential disadvantages I might not be aware of.  

I am running three times a week at the moment (total 25-30 km), but also go to the gym and swim regularly, so there isn't much scope for increasing the number of runs.

Updates:

19/04/2023 - I've run my first half-marathon (2:16:43) without a real problem, I'll try it again next month and report back.  Hopefully the lack of an answer (at time of writing) suggests that my plan isn't too daft!

23/05/2023 - Run second half-marathon (2:18:06,but trail rather than on track and lower average heart rate).  Felt much easier than last time, no immediate problems.