Due to the distances involved, 2015 SkyMiles is spectacularly bad for international travel flying economy - or really even domestic travel for anyone west of the Mississippi unless they're commuting on short regional hops. For example:

(All 1 week adv purchase fares are actual quotes from Delta.com for round trip flights departing Monday March 2nd as of Feb 19th. Historical data is from faremeasure.com. Both actual fares overestimate earnings because they include taxes.)

SEA-NRT - Breakeven $1900 for general member, $1950 for Diamond; 1 week adv purchase $1123
SEA-AMS - Breakeven $1950 for general member, $2000 for Diamond; 1 week adv purchase $1456
SEA-ATL - Breakeven $875 for general member, $900 for Diamond; Average fare $547; 1 week adv purchase $668
MSP-LAX - Breakeven $625 for general member, $650 for Diamond; Average fare $515; 1 week adv purchase $398
SEA-LAX - Breakeven $400 for general member, $400 for Diamond; Average fare $315; 1 week adv purchase $247
SEA-PDX - Breakeven $200 for general member, $200 for Diamond; Average fare $251; 1 week adv purchase $224
SFO-LAX - Breakeven $200 for general member, $200 for Diamond; Average fare $262; 1 week adv purchase $148

Note the real breakeven values are actually worse, because these calculations assume nonstops: in many cases a real itinerary would involve connections on these routes, which would increase the 2014 earnings.

So, yeah. Unless you're flying SEA-PDX, or booking very last minute fares, or flying F, you're not coming out ahead on any of these routes in almost all cases.