Kelechi has played 1431 minutes for City, scoring 17 (actually 18 but one horrible mistake by the linesman) & assisting 8. Giving a goals/min ratio of 84 minutes per goal & a goals/assists per minute ratio of every 57 minutes.
For Nigeria Kelechi has 3 goals, 2 assists in 282 minutes, a goals/min ratio of 94 minutes per goal & goals/assists per minute ratio of every 56 minutes. Impressively similar to those in an obviously stronger team at City.
As a comparison Rashford has 10 goals, 2 assists from 1917 minutes for United, giving him a goals/min ratio of 192 minutes per goal & goals/assists per minute ratio of every 160 minutes.
So on stats alone Iheanacho outscores Rashford at a 2:1 rate, and scores/assists at a rate of 2.8:1 compared to Rashford.
I think they're both fantastic young talents with big futures, but quite different in terms of style - I think it's fair to say Iheanacho is a more natural goalscorer with more end product as it stands, and Rashford is more of a dribbler & threat from other areas such as the wing.