Um, yeah?
iPhone 5S: 3.95 ounces
iPhone 6: 4.55 ounces
iPhone 6 Plus: 6.07 ounces
Going from a 5S to a 6 is just a 15.2% increase in weight, however going from a 5S to a 6 Plus is a 53.7% increase in weight.
So yeah, going from a 5S to a 6 Plus (which is what I did, as well as OP) is a dramatic increase in weight.
Even going from 6 to a 6 Plus is a 33.4% increase in weight.
So yeah. Heavy.
Are you a smurf? J/k
Just seems like 6 ounces is never heavy since you are only holding your phone for a few mins at a time.