Long songs are often superb. To give a (non folk) example, The Sweet had a hit in 1978 with Love Is Like Oxygen which was a decent 3 minute pop song. However, the album version has a tremendous instrumental passage which increases the length of the song to about 7 minutes and turns in into an absolute classic.

Trust your own judgement. If you enjoy the longer passages, chances are so will a large proportion of your audience.