110 vs. 310, 310 vs. 315
Your 110 is basically a 310 - same heads, same IQ, same speed, same maintenance. On the 110 the onboard RIP has been simplified and you have smaller ink cartridges as has been pointed out (400ml vs. 775ml) - which = a higher ink CPC on the 110 vs. 310. But as someone points out - still around .27 at list price for a 110 CPC vs. .22 for a 310 so very competitive relative to other 440 ml based machines.
As far as the 310 vs. the 315 now - all print economics are the same, inks, heads, maintenance, CPC etc. - differences in new 3X5 series are: Optical Media Advance Sensor (OMAS), Auto X Cutter, Variable Front tension kit for TUR (Optional), and Continuous printing (you can upgrade your 310 to this for NC - requires current FW and RIP) The 315 price was also lowered by $1,000 so you may consider this as well. Hope this helps.