Originally Posted by afv011
Your Sigil 0.13 binary is probably in /opt. In my case, the problem was that Sigil's binary for 0.13 was in /opt and 0.15 was trying to create a "sigil" folder in the same place, hence the install issue I was experiencing. I deleted the 0.13 binary and 0.15 was happy.
The sigil 0.13 binary was in /usr/local/bin as it turned out