iPhone 6s and 6s Plus has gone little heavier compared to iPhone 6 and 6 Plus, and its because of some heavier material used in the recent models. You must be thinking about the Aluminum 7000 that is used to get rid of bending issue, but it’s not correct. Aluminum 7000 helped iPhone 6s to decrease 1g, but increased only 3g in iPhone 6s Plus.
Weight and Thickness
iPhone 6 : Weight – 129 grams, Thickness – 6.9 mm
iPhone 6s: Weight – 143 grams, Thickness – 7.1 mm
iPhone 6 Plus : Weight – 172 grams, Thickness – 7.1 mm
iPhone 6s Plus : Weight – 192 grams, Thickness – 7.3 mm
iPhone 6s is 14 grams and 6s Plus is 20 grams heaver than previous models, and both the new models are 0.2 mm thicker than before. Display is the major reason to increase the thickness and weight. The new display has brought 3D touch that usage the sensor to understand the firmer and lighter tap. So the new display in iPhone 6s is 17 grams heaver than before. In the same way, it’s 21 grams heavier in iPhone 6s plus compared to 6 Plus.