Our train gets to Poroy at 7:05 pm and the plane leaves at 8:15. Do we have enough time to make it on time?
Extremely unlikely. Just the driving time is at the very least 25 mins, often 40 mins or so. At that hour, it will be closer to the latter since it's the morning rush hour. Google Maps suggests 40 mins driving time.
Add to that the time to get out of the train, at least 5 mins, and lineup for a taxi. It's busy with a small entrance, so the taxi leaving will take several minutes just exiting.
On the airport end you need to at least go through security, assuming you checked in already and have no luggage to drop off first. The gate usually closes 15 mins before departure, depending on the airline it could be up to 45 mins, and luggage must be dropped 45-60 mins in advance.
Finally, the train in Cusco is not that timely, even though not by much, all this stacks the odds against you. Even though the schedule is precise, it often arrives 5-20 minutes late.
Rome2Rio shows that private vehicle (for hire) is the only way to get from the train station to the airport, some 20 km, and suggest that it can take about 15-20 minutes.
Depending on your flight arrangements, you may be able to make the connection (or need to make some adjustments). As it is, it may be too tight.
Here are the check in times for carriers that fly from Cusco:
LATAM: Domestic 90 minutes before departure, international 3 hours.
Avianca: Domestic 1 hour 45 minutes, international 2 hours
Peruvian Airlines: 60 minutes
Star Peru: you must arrive at the gate forty (40) minutes before the departure time.