Yes, a 1.5 hour layover should be plenty of time... assuming your original flight gets in on time. Our recent experience, we learned the hard way to leave more time for a layover in case of delay to the original flight. Perhaps with them adding more daily flights MIA-EIS, the issue will improve, but what we found is that if your flight to MIA is delayed, your chances of getting on a later flight to EIS are slim to none (even though there were seats available, they wouldn't let us on the later flight due to weight restrictions, we had to fly to STT instead in order to get there same day).
While less convenient, If there are multiple flight options from your origin point, don't take the closest one to the EIS departure, take the earlier one. That way, if the flight is delayed, you can still hop on the later one, or still get in with enough time to make the connection.
I know I worded that awkwardly, but hope it makes sense.
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