Optimize measure - Summarize is slowing down the performance

Good morning,

I have a matrix in a Power BI Report.

On row level (lowest level) I have this measure ([_WinkelAandeel (Rijniveau) (€)]: 

VAR aandeel = SUMX(SUMMARIZECOLUMNS(FiliaalAfsluit[SK_Datum], FiliaalAfsluit[SK_Partij], FiliaalAfsluit[WinkelAandeel]), DIVIDE(FiliaalAfsluit[WinkelAandeel],100))
VAR result =
DIVIDE([_Omzet (€)], aandeel)
Return result

Then on the other levels in the rows, I need to sum up the values of the above measure.

I used this measure to achieve the desired result:

IF(ISINSCOPE(DatumVerkoop[Datum]), [_WinkelAandeel (Rijniveau) (€)], SUMX(SUMMARIZE(FiliaalAfsluit, FiliaalAfsluit[SK_Datum], FiliaalAfsluit[SK_Partij], FiliaalAfsluit[WinkelAandeel],"Subtotal", [_WinkelAandeel (Rijniveau) (€)]), [Subtotal]))

However this measure is too slow. 

Any ideas on how to optimize it?

Thank you in advance