Without seeing the rest of your roster, this seems like a classic win now-mortgage the future a bit trade. You fill a need while not giving up anything that will hurt you this year. Teheran is a great prospect, but slowly some experts are souring on him compared to others. In fact I think Goldstein, or Law, or someone like that just ranked Arodys Vizcaino ahead of him. It's not a huge deal, but I mention it because of opportunity cost. I find that in most leagues like this there are usually similar, or slightly less valuable prospects to be had on the ww. If you have someone to drop and still want to, you can make this deal AND not give up much in terms of future value. My guess is that you'd want someone near ML ready. Is Vizcaino available? Another guy that I think will be up soon and contributing, though not a blue chip prospect (yet?) is Brad Peacock. Maybe you can look into him.
If you like, put a list together of available minor leaguers and let me help you pick someone. Please return the favor:viewtopic.php?f=26&t=435517&p=3433242#p3433242