Before I forget, have you had a chance to check out @gregcaporaso's SILVA 132 post?
Hi @LauraMason - did you happen to edit or modify the SILVA_132_QIIME_release/taxonomy/16S_only/97/taxonomy_7_levels.tsv file at all? I ask because I just downloaded a fresh copy of SILVA 132 and ran the exact same command (without modifying any of the SILVA files) and it imported in about 1 second. The only thing that comes to mind besides that is I ran that import command in a 2018.2 environment (you appear to be running 2017.12), but I can't recall any changes to these formats that would account for that.
Looking forward to your response - we will get to the bottom of this! Thanks! 