How does the LIP package which is standard on the A320NEO enable to approach at a slower speed?
On first impressions, all of those (except the nacelle strake and the fillet) seem to modify the high lift system (slats/flaps), presumably to optimise air flow in the gaps between slat and main wing or main wing and flaps. This is probably done to increase the maximum attainable angle of attack or lift coefficient, which will reduce stall speed and thus allow a lower approach speed.

The nacelle strakes normally are used to optimise flow around the engine nacelle at high angles of attack, either to prevent premature wing stall around the nacelle or to at least improve aircraft handling qualities by preventing localised flow separation at the nacelle. Adding another strake on the other side will, I imagine, again allow a slightly higher angle of attack to be sustained and thus will lower the permitted approach speed.

The wing body fairing modification most probably, too, will allow a more optimal local air flow.

All of this is my speculation based on the list of changes in the question; I don’t have additional knowledge on this particular aircraft performance package.