I'll share my thoughts on this. Your recent half marathon time equates to a marathon time that is well under 3:20. Your training mileage is low so it makes it hard to use that half marathon time to justify something close to a 3:15 time. On the other hand you are relatively young so who knows how you will do in the later miles of the race. If you spent more time in your training and added more mileage and quality you could be capable of a sub 3:15 time. However we need to deal with your current training and fitness. What is your goal here? If it is really a BQ, then go for it. Seriously! A BQ -5:00 might get you there. Given the effect of the pandemic on races your chances might be good if your are in the -5:00 range. When I made my second attempt at BQ my goal was -10:00 which pretty much guarantees you will get in.
Back to Chicago as the race and if your goal is a BQ. There is a 3:25 pace group in corral D. I think you should go with that and adjust if you find it necessary. If you are capable for something close to a 3:15 based upon your half marathon time I don't think it is that unreasonable to handicap that by 10min based upon the weather forecast and a 48mpw average. If you crash and burn, it is unlikely that you would have made that BQ. Chicago is really flat so there are no hills at the end that are going to take the wind out of your sails. Although there is some wind in the current forecast so that might be a factor. I need to look go back and look at the wind direction to see how that might impact the race.
I will be running Chicago and I am disappointed by the weather forecast, but I am not surprised because Chicago has been notorious for having warm weather. For my true goal race I chose one that has been more consistently had better weather.
Whatever you decide and whatever happens, Good luck!