Macbook Pro 60w charger for 15inch

I am using my 2011 15 inch Macbook Pro right now, left my charger at home and am not able to retrieve it right now. I have to get some work done so I am using a friends 60W charger that they actually use for their late 2008 model 15inch Macbook Pro. I have read that it will work but the charging takes longer and it may not charge it fully. But I just want to make sure that it wont be doing any serious damage to my laptop. This thing cost waaay too much money to just let it get messed up over something so small. If anyone has had any experience using a lower wattage charger on a higher wattage machine please let me know your experience. I see it as not doing harm as its only under powering the machine, not over powering. Where I would feel unsafe using a 85W on a 13inch that takes a 60W charger as you could fry it from overcharge. Thanks in advance.

-Brandon