summarize performance

hello, 
I made a measurement using the summarize function as below, but the speed is slow, so please help me if there is any way to improve it.

a : Cust_ID Summarize with one exter_id (Order_ID) based on the customer type "Rewards" based on Cust_ID
b : Check the quantity purchased by product using cust_ID of 'a'

# Purchase_1_A = 
var a =
FILTER(
SUMMARIZECOLUMNS('anl_dm_loyalty_sales_point_mart'[saguid])
                            ,CALCULATE(DISTINCTCOUNT('anl_dm_loyalty_sales_point_mart'[exter_id])
                                        ,'anl_dm_loyalty_sales_point_mart'[Cust_Type] = "Rewards"
                                        ,ALL('std_product_loyalty'[product_name])
                                        )=1)
							
var b = 
SUMMARIZE(CALCULATETABLE('anl_dm_loyalty_sales_point_mart'
                                        ,'anl_dm_loyalty_sales_point_mart'[Cust_Type] = "Rewards"
                                        ,'anl_dm_loyalty_sales_point_mart'[saguid] IN a
                                        )
                            ,[saguid]
                            ,[obj_id]
                            ,"Qty",CALCULATE(SUM('anl_dm_loyalty_sales_point_mart'[quantity])
                                                ,FILTER('std_product_loyalty','std_product_loyalty'[product_name] <> BLANK()))
)
                                                
Return
SUMX(b,[Qty])