Between the 1987-88 and 1990-91 seasons, the Detroit Pistons had the best defensive rating by a team in the playoffs when playing 15+ games, with a 104.9 rating.

lowest team drtg 1987-88 to 1990-91 playoffs with 15 gp minimum

TEAM	GP	DRTG	MPG	PPG	RPG	APG	SPG	BPG	TPG	FGM	FGA	FG%	3PM	3PA	3P%	FTM	FTA	FT%	MIN	PTS	REB	AST	STL	BLK	TOV	PF
Detroit Pistons	75	104.9	242.0	100.7	44.2	21.7	6.2	4.4	13.3	38.3	82.6	46.4	2.3	7.1	31.9	21.8	29.0	75.1	18,150	7,555	3,315	1,631	467	331	998	1,909
Chicago Bulls	60	106.1	241.3	100.7	40.9	23.9	8.4	4.3	14.4	38.6	80.6	47.8	2.6	7.9	32.6	21.0	27.4	76.7	14,475	6,039	2,456	1,432	503	257	862	1,473
Phoenix Suns	32	107.5	240.0	110.4	45.7	24.6	7.7	5.0	15.4	41.0	87.4	46.9	2.4	7.9	30.7	26.0	32.6	79.9	7,680	3,533	1,463	787	247	160	493	744
Utah Jazz	28	108.7	240.0	104.0	41.5	24.9	7.3	5.4	15.3	38.8	82.6	46.9	2.5	7.0	35.7	24.0	30.2	79.4	6,720	2,911	1,161	698	205	152	427	708
San Antonio Spurs	17	108.7	244.4	113.5	45.4	29.0	9.2	5.6	17.1	45.8	92.8	49.3	0.9	4.4	20.0	21.1	29.4	71.8	4,155	1,930	771	493	156	96	291	442
Cleveland Cavaliers	15	109.1	241.7	101.5	40.5	24.7	6.7	6.1	14.7	38.9	78.7	49.4	1.8	6.1	29.3	21.9	29.5	74.3	3,625	1,522	607	371	100	92	221	313
Portland Trail Blazers	44	109.5	242.3	105.7	43.8	23.7	8.5	4.6	15.5	39.5	87.4	45.2	2.9	9.1	32.1	23.7	32.3	73.4	10,660	4,650	1,925	1,041	372	204	682	1,126
Los Angeles Lakers	67	110.8	240.7	106.3	40.5	24.9	7.3	4.9	14.6	39.9	80.7	49.4	2.9	8.4	34.9	23.6	30.0	78.5	16,130	7,119	2,714	1,667	489	329	977	1,444
Houston Rockets	15	111.0	240.0	101.0	40.7	22.7	8.4	5.1	15.3	38.9	84.7	45.9	2.9	8.9	32.3	20.3	27.2	74.5	3,600	1,515	611	340	126	77	230	349
Boston Celtics	36	111.8	242.8	106.6	40.8	25.4	6.3	4.5	14.5	39.9	81.5	49.0	1.6	5.7	28.4	25.2	31.0	81.2	8,740	3,838	1,469	915	228	161	522	835
Seattle SuperSonics	18	113.0	240.0	105.8	42.6	23.8	7.8	5.7	15.8	41.0	86.7	47.3	2.5	9.2	27.3	21.3	28.8	74.1	4,320	1,905	766	428	141	103	284	502
Philadelphia 76ers	21	113.2	242.4	102.1	39.0	23.5	7.2	4.7	14.1	38.0	79.1	48.0	2.5	8.0	31.5	23.7	30.7	77.3	5,090	2,145	820	494	152	98	297	456
Golden State Warriors	17	113.9	241.5	112.3	39.8	22.5	9.1	7.2	13.6	43.3	90.7	47.7	3.8	12.9	29.7	21.9	27.0	81.0	4,105	1,909	676	382	155	122	231	462
Denver Nuggets	17	114.3	240.0	111.8	42.9	24.1	7.4	4.2	12.5	42.5	94.3	45.0	3.4	11.2	29.8	23.5	28.2	83.1	4,080	1,900	730	410	126	72	212	436
Atlanta Hawks	22	114.4	242.3	104.8	40.6	24.0	6.9	4.7	12.2	38.8	82.8	46.8	1.8	6.9	26.3	25.4	32.0	79.3	5,330	2,305	894	529	151	104	269	551
Dallas Mavericks	20	114.5	240.0	106.8	44.1	23.6	7.5	5.2	15.4	42.3	85.8	49.2	1.7	6.1	27.9	20.6	27.2	75.7	4,800	2,135	881	472	150	104	307	435
New York Knicks	26	115.1	241.9	102.5	40.8	25.7	7.8	3.9	15.7	39.1	83.7	46.7	3.5	9.7	36.0	20.8	27.3	76.2	6,290	2,666	1,062	667	204	102	408	657
Milwaukee Bucks	21	116.0	243.6	101.1	37.7	23.6	6.9	2.9	14.1	37.4	79.4	47.1	2.6	8.1	31.6	23.8	30.0	79.2	5,115	2,124	791	495	144	60	296	555