It's from 1919, we don't have exact dates of issue.
Fischer catalogue number Cp30, type "b". Higgins & Gage #30
The 15 fennig stamps & cards were printed in 3 different types differentiated by the 2 lines on the upper right under the "15".
Type "a" has 1 short +1 long line
Type "b" has 2 short lines
Type "c" has 1 short +1 long line extending right across the value tablet.
This is found on the pre-printed postal cards with & without the value "F" in the value tablet.
Type "a" to "c", top to bottom
15fen was the domestic Polish postcard rate in 1919 in the Northern part of Poland.
The first 15fen card of the eagle in a shield type was the word "Pocztowka" (postcard) & indica overprinted on old German postcards.
1919 Aug 1, Warsaw, local postcard
The card was forwarded to Grodzisk where it was backstamped Aug 8 1919
& returned to Warsaw. The 2 handstamps are "Nieznany (Unknown) & "Zwrot" (Return)
Next up was a completely printed up card with denomination "F" for fennigs printed in the tablets
1919 30 Sept. Warsaw to Switzerland. Additional 15f stamp. Censorship mark
There were hostilities in the North West of Poland around the Poznan area, military censorship was in force
Finally, in 1920, with the unification of the Polish currency, the denomination "F" was removed & the cards were valid for use in the whole of Poland.
1920 9 Mar. Warsaw to France. Int. postcard rate was 20f so 5 centimes Post-due applied in France
This is a simplified overview of the cards, they come in shades of red, carmine & rose, as well as 3 different types of horizontal dotted lines, thin, thick or a combination of thick & thin. My 10 year-old Fischer catalogues yours at 70zloty, current market value is $10-15.