60f is 15 Celsius yeah? That's not super cold if I got my conversions right.
I don't know anything about heaters for birds because I've never really needed one but as long as it's safe for birds, and just safe generally to be left on over night, I don't think there's any reason not to get one. Your bird would probably be more comfortable, and you too.
I think that just as not all humans are the same birds are not always the same either. My bird just never gets sick. I live in Australia and it is a particularly cold winter right now, particularly at night. But he is such a strong birdie.
It is colder than 15 Celsius right now at night.
Yeah it's like 15 Celsius here in perth australia in the middle of the day, I think it's only been like 6 degrees at night lately. Mine just get covered up with a birdie night cover and they're doing fine.
I wouldn't say that 15 celcius is cold, but if you feel cold at this temperature and feel that your bird might be cold, I'd use the heater. In NZ it's winter time and in my area it's been around 10 degrees or less during the day, and 1 - 5 degrees at night (it's much colder in the south though, they've just had over a metre of snow). We have a fireplace that generally heats the whole house, but my room is very chilly, so I have an oil column heater that's on most of the time. The 'tiels get a few thick blankets over their cage at night to keep them warm. They don't seem to notice it's winter; Henry generally thinks it's spring the majority of the time.
I'm in Adelaide, and it is between 4-6 degrees most nights at the moment where I am - maybe a bit colder. Rocky isn't covered at nights (he is happy unconvered and tends to get a bit upset over covers) and neither are my aviary budgies outside. They are all doing fine and don't seem bothered by the cold at all.