These mirco snowflakes are about 15mm across and were generated with my Snowflake Machine: http://www.thingiverse.com/thing:1159436.The models are optimized for printing on an Ultimaker 2 with ABS and the special .25mm nozzle with the Olsson block, at "Ulti quality" 0.04mm layer height. If you want very small snowflakes that are already tested and ready to go, then print these.But it's much more fun to go make your own, so go do that at the Snowflake machine link above! For 15mm snowflakes, set the "Target Diameter" to 15 in the "Global Size Settings". For this size you'll have to reduce to 4-5 steps and keep the thickness of the strands down by setting low values for "fat" and "organic". You may also have to keep "fuzzy" and "full" parameters to a minimum.More about the Olsson block:  https://www.youtube.com/watch?v=exwy4soZ_3U