Thank you so much to everyone for the replies! I've worked really hard to get my employer to look into better options for our plan. I work for a small and newish non-profit and was able to get our CFO to get a quote for us from Vanguard. Due to our current plan assets being small, Vanguard's fees are only slightly lower currently but become hugely lower for us as our plan assets increase. I was very surprised that having this data in front of him, our CFO wasn't on-board for making the switch since our plan assets are increasing every month. He did say that John Hancock, our current plan provider, had told him that Vanguard doesn't offer the range of options that they do and he seemed to think this was a valid concern (I don't, I think JH is just trying to hold onto business). I've also tried using calculators that show how investment costs eat away at earnings over time as a way to show my employer why this is an important thing to fix in our plan, and, since those staggering graphs and numbers didn't do it, I don't know what will.
Based on the replies I received here, I have asked my employer whether our plan allows for in-service withdrawals. Whether it does our not, it seems like the best way for me to proceed is to continue maxing our my Roth IRA and also my HSA and then to, despite the high fees, invest as much as possible in my 401k rather than in a taxable account (I do think that either, 1) I will have left this job within 10 years, or 2) They will have improved the 401k plan).
If the above is the best strategy, I just have one other question: given that I am in the 15% tax bracket, does it make sense for me to use our Roth 401k option or the Traditional 401k? It was always an easy decision for me to go Roth with my IRAs but what I've been reading about Roth conversion ladders seems to indicate that I could rollover a traditional 401k to a traditional IRA when I leave my job and then slowly convert the traditional IRA to a Roth year by year and not pay taxes. Is that accurate? I just want to make sure that I am choosing the best 401k type given that the plan itself is already handicapping the earnings significantly with its fees. Thank you to everyone! :)